Combustor Nozzle/Premixer with Curved Sections

ABSTRACT

An apparatus for premixing fuel and air prior to combustion in a gas turbine engine includes an annular fuel passage receiving fuel from a fuel source. The annular fuel passage includes a fuel plenum and has a wave shape with a peak section surrounded by trough sections. An annular air passage surrounds the annular fuel passage. The annular air passage receives air to be mixed with the fuel in the fuel passage for downstream combustion. A plurality of swirler vanes are disposed in the annular air passage adjacent the fuel plenum.

BACKGROUND OF THE INVENTION

The invention relates to premixing fuel and air prior to combustion in agas turbine engine and, more particularly, to a combustornozzle/premixer including curved sections to improve mixing.

Gas turbine engines generally include a compressor for compressing anincoming airflow. The airflow is mixed with fuel and ignited in acombustor for generating hot combustion gases. The combustion gases inturn flow to a turbine. The turbine extracts energy from the gases fordriving a shaft. The shaft powers the compressor and generally anotherelement such as an electrical generator.

Cold air from the flow sleeve enters into the combustor headend regionand is distributed among a plurality of nozzles. Generally, air passesthrough an inlet flow conditioner (IFC) and becomes uniform incircumferential direction. Subsequently, it is rotated by axially placedvanes, and fuel is injected into the flow through holes in the vanes forpremixing of fuel and air.

The exhaust emissions from the combustion gases generally are a concernand may be subject to mandated limits. Certain types of gas turbineengines are designed for low exhaust emissions operation, and inparticular, for low NOx (nitrogen oxides) operation with minimalcombustion dynamics, ample auto-ignition, and flameholding margins.

Low NOx combustors typically include a number of combustion canscircumferentially adjoining each other around the circumference of theengine. Each can may have one or more fuel air mixers or nozzlespositioned therein. Nozzles use swirling air to mix fuel and air, andhence are referred to as “swirlers.” The swirlers may have a number ofcircumferentially spaced apart vanes for swirling and mixing thecompressed airflow and the fuel as they pass therethrough.

The combustor nozzle serves to provide fuel air premixing with minimumpressure losses. It would be desirable to perform the premixing functionover a shorter distance and more efficiently. With more fuel-air mixingover a shorter distance, combustion emissions can be reduced.Additionally, existing swirler vanes typically include internal passagesfor fuel, and the swirler vanes are thus larger in size than desired andmore expensive to manufacture. It would be desirable to simplify theconstruction and eliminate the internal passages in the swirler vanes.

BRIEF DESCRIPTION OF THE INVENTION

An apparatus for premixing fuel and air prior to combustion in a gasturbine engine includes an annular fuel passage receiving fuel from afuel source, an annular air passage surrounding the annular fuelpassage, and a plurality of swirler vanes disposed in the annular airpassage adjacent a fuel plenum section. The annular fuel passage has anupstream passage, a neck passage narrower than the upstream passage, andthe fuel plenum section that curves from the neck passage to a widerpassage. The annular air passage receives air to be mixed with the fuelin the fuel passage for downstream combustion.

In another exemplary embodiment, a combustor includes a casing, and aplurality of nozzles disposed in the casing. Each of the nozzlesincludes the structure of the apparatus for premixing fuel and air priorto combustion in a gas turbine.

In still another exemplary embodiment, an apparatus for premixing fueland air prior to combustion in a gas turbine engine includes an annularfuel passage receiving fuel from a fuel source. The annular fuel passageincludes a fuel plenum and has a wave shape with a peak sectionsurrounded by trough sections. An annular air passage surrounds theannular fuel passage. The annular air passage receives air to be mixedwith the fuel in the fuel passage for downstream combustion. A pluralityof swirler vanes are disposed in the annular air passage adjacent thefuel plenum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view of a gas turbine engine;

FIG. 2 is a sectional view of the combustor nozzle/premixer;

FIG. 3 is an end view of the combustor nozzle; and

FIG. 4 is a close-up view showing the swirler vanes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cross-sectional view of a gas turbine engine 10. The gasturbine engine 10 includes a compressor 20 to compress an incomingairflow. The compressed airflow is then delivered to a combustor 30where it is mixed with fuel from a number of incoming fuel lines 40. Thecombustor 30 may include a number of combustor cans or nozzles 50disposed in a casing 55. As is known, the fuel and the air may be mixedwithin the nozzles 50 and ignited. The hot combustion gases in turn aredelivered to a turbine 60 so as to drive the compressor 20 and anexternal load such as a generator and the like. The nozzles 50 typicallyinclude one or more swirlers.

FIG. 2 is a sectional view of the combustor nozzle/premixer according topreferred embodiments. The nozzle 50 is one of several disposed in anarray within the casing 55. The nozzle 50 includes an annular fuelpassage 62 receiving fuel from a fuel source. The annular fuel passage62 includes an upstream passage 64, a neck passage 66 narrower than theupstream passage 64 as shown, and a fuel plenum section 68 that curvesfrom the neck passage 66 to a wider passage. The fuel passage defines awave shape as shown with a peak section surrounded by trough sections.An annular air passage 70 surrounds the annular fuel passage 62 andreceives air to be mixed with the fuel in the fuel passage 62 fordownstream combustion. An entrance 71 of the air passage 70 may berounded as shown. A plurality of swirler vanes are disposed in theannular air passage 70 adjacent the fuel plenum section 68.

The fuel plenum section 68 includes fuel holes in the annular fuelpassage 62. In an exemplary embodiment, the nozzle includes at least 40fuel holes 74. Preferably, the fuel holes 74 are disposed in the widerpassage (widest section) of the fuel plenum section 68. As shown in FIG.2, the fuel plenum section 68 narrows downstream of the wider passagesuch that the wider passage defines a peak section. The fuel holes 74are preferably disposed in the peak section. Additionally, the swirlervanes 72 are disposed surrounding the annular fuel passage 62 adjacentthe peak section. The fuel holes 74 are positioned between the swirlervanes. With continued reference to FIG. 2, the fuel holes 74 may bepositioned upstream of a trailing edge of the swirler vane 72 such thatthe fuel has sufficient axial velocity, which reduces the risk offlameholding.

By virtue of the curved fuel passage 62 and correspondingly curved airpassage 70, an exterior surface of the annular air passage is similarlycurved substantially corresponding to the fuel plenum section 68. Thecurved exterior surface 76 provides for slight compression/diffusionwith the casing 55 and thereby reduces incoming circumferentialnon-uniformities. That is, along with the surface of the casing 55, thenozzle 50 forms a convergent/divergent passage that acts a flowconditioner. Non-uniformities from the compressor due to the 180° turnof the air may be smoothed out efficiently. Overall, air will bedistributed without significant non-uniformities via the outsidecurvature and rounded entrance.

In contrast with the prior designs, instead of an axial swirler, thestructure of the described embodiment is curved or wavy. Air from theheadend passes through the rounded entrance 71 to maintaincircumferential uniformity. The air in the annular air passage 70 flowsup the curved section, which further serves to remove non-uniformities.Subsequently, the air passes through the vanes 72 and is mixed with fuelentering the air path via the fuel holes 74. Since the vanes do notinclude passages for fuel, the vanes can be made highly aerodynamic.Additionally, the vanes can be made about 50% shorter than existingvanes, which provides extra fuel/air premixing length or alternatively,the nozzle can be shortened. Additionally, the vanes can be made thinnerin the absence of the fuel passages, which serves to decrease theoverall weight of the swirler. The curved or wavy shape enables air totravel radially upward and to come down at fuel injection. The resultingradial current facilitates fuel and air mixing (radial current is notpresent in an axial swirler).

Fuel is injected from the downstream curvature of the nozzle but stillat a high radius such that premixing is efficient. The fuel plenumbeneath can be made diffusive to decrease pressure variations. Multiplefuel hole locations between two vanes or downstream of the vanes can beprovided. Hole locations should be such that fuel from multiple holesdoes not mix, and the fuel stream is not directed towards the trailingedge of the vanes. As noted, by placing the fuel holes in the region ofslightly high axial velocity, a risk of flameholding is reduced. Thestructure effects a slight radial current, resulting in early mixing.Moreover, there is no flow conditioning device needed, and the overallpressure drop reduces to a greater extent.

The shorter and aerodynamic vanes along with the rounded entrance makethe nozzle highly efficient in terms of pressure drop. The only pressuredrop will be due to the rotation of the flow in the burner tube.Moreover, since the swirler is independent of the vane core and cavity,it can be made shorter, providing opportunities to reduce the length ofthe swirler or provide for better mixing with the same length. On theexterior of the nozzle, with the convergent-divergent passage, thedesign filters out non-uniformities in CDC air after flow sleeve exit.Since the compression-diffusion is smooth, associated pressure lossesare minimized.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. An apparatus for premixing fuel and air prior tocombustion in a gas turbine engine, the apparatus comprising: an annularfuel passage receiving fuel from a fuel source, the annular fuel passagehaving an upstream passage, a neck passage narrower than the upstreampassage, and a fuel plenum section that curves from the neck passage toa wider passage; an annular air passage surrounding the annular fuelpassage, the annular air passage receiving air to be mixed with the fuelin the fuel passage for downstream combustion; and a plurality ofswirler vanes disposed in the annular air passage adjacent the fuelplenum section.
 2. An apparatus according to claim 1, wherein the fuelplenum section comprises fuel holes in the annular fuel passage, thefuel holes being disposed in the wider passage of the fuel plenumsection.
 3. An apparatus according to claim 2, wherein the fuel plenumsection narrows downstream of the wider passage such that the widerpassage defines a peak section, and wherein the fuel holes are disposedin the peak section.
 4. An apparatus according to claim 3, wherein theswirler vanes are disposed surrounding annular fuel passage adjacent thepeak section.
 5. An apparatus according to claim 4, wherein the fuelholes are disposed between the swirler vanes.
 6. An apparatus accordingto claim 2, comprising at least 40 fuel holes.
 7. An apparatus accordingto claim 1, wherein an exterior surface of the annular air passage iscurved substantially corresponding to the fuel plenum section, thecurved exterior surface reducing incoming circumferentialnon-uniformities of input air.
 8. An apparatus according to claim 1,wherein the fuel plenum section comprises fuel holes in the annular fuelpassage, the fuel holes being disposed upstream of a trailing edge ofthe swirler vanes such that the fuel has sufficient axial velocity. 9.An apparatus according to claim 1, wherein an entrance to the annularair passage is rounded.
 10. A combustor comprising: a casing; and aplurality of nozzles disposed in the casing, wherein each of the nozzlesincludes: an annular fuel passage receiving fuel from a fuel source, theannular fuel passage having an upstream passage, a neck passage narrowerthan the upstream passage, and a fuel plenum section that curves fromthe neck passage to a wider passage, an annular air passage surroundingthe annular fuel passage, the annular air passage receiving air to bemixed with the fuel in the fuel passage for downstream combustion, and aplurality of swirler vanes disposed in the annular air passage adjacentthe fuel plenum section.
 11. A combustor according to claim 10, whereinthe fuel plenum section comprises fuel holes in the annular fuelpassage, the fuel holes being disposed in the wider passage of the fuelplenum section.
 12. A combustor according to claim 11, wherein the fuelplenum section narrows downstream of the wider passage such that thewider passage defines a peak section, and wherein the fuel holes aredisposed in the peak section.
 13. A combustor according to claim 12,wherein the swirler vanes are disposed surrounding annular fuel passageadjacent the peak section.
 14. A combustor according to claim 13,wherein the fuel holes are disposed between the swirler vanes.
 15. Acombustor according to claim 10, wherein an exterior surface of theannular air passage is curved substantially corresponding to the fuelplenum section, the exterior surface of the annular air passage and aninterior surface of the casing defining a headend air passage, whereinthe headend air passage is shaped to reduce incoming circumferentialnon-uniformities of input air.
 16. A combustor according to claim 15,wherein an entrance to the annular air passage is rounded.
 17. Anapparatus for premixing fuel and air prior to combustion in a gasturbine engine, the apparatus comprising: an annular fuel passagereceiving fuel from a fuel source, the annular fuel passage including afuel plenum and having a wave shape with a peak section surrounded bytrough sections; an annular air passage surrounding the annular fuelpassage, the annular air passage receiving air to be mixed with the fuelin the fuel passage for downstream combustion; and a plurality ofswirler vanes disposed in the annular air passage adjacent the fuelplenum.
 18. An apparatus according to claim 17, wherein the fuel plenumcomprises fuel holes in the annular fuel passage.
 19. An apparatusaccording to claim 19, wherein the fuel holes are disposed in the peaksection.